1. Field of the Invention
The present invention relates to a combo-jack detecting circuit for use in an audio codec. More particularly, the combo-jack detecting circuit of the present invention is configured to detect a jack type of a combo-jack.
2. Descriptions of the Related Art
Many audio apparatuses currently available in the market need to have a simultaneous audio output and input function (e.g., headsets). Most of the existing audio apparatuses have an audio input jack and an audio output jack, which are originally independent from each other, and then integrated into a single combo-jack for convenience. The combo-jack of such an audio apparatus with four terminals is normally provided with a left-sound channel audio output terminal, a right-sound channel audio output terminal, an audio input terminal and a ground terminal. Only in this way, can the audio apparatus play, via a speaker thereof, a sound signal transmitted from an audio codec and output the received sound signal via the audio input terminal to the audio codec for subsequent processing.
Accordingly, to meet the aforesaid requirements, the combo-jacks currently available adopt four terminals mostly in the form of TRRS (i.e., a terminal Tip, a terminal Ring1, a terminal Ring2 and a terminal Sleeve). To make a combo-jack downward compatible with a common apparatus (e.g., an earphone) with only an input jack, the terminal Tip and the terminal Ring1 of the combo-jack are fixedly used as the left-sound channel audio output terminal and the right-sound channel audio output terminal respectively. However, on the other hand, the audio input terminal or the ground terminal of the combo-jack is not mandatorily specified to necessarily correspond to the terminal Ring2 and the terminal Sleeve, so when a designer of audio systems integrates an audio codec with a combo-jack of an audio apparatus, the audio output terminals, the audio input terminal and the ground terminal of the audio codec usually must be designed to match those of the combo-jack.
In more detail, when the combo-jack of the audio apparatus uses the terminal Ring2 as the ground terminal and uses the terminal Sleeve as the audio input terminal, the designer of audio systems must design the circuit of the audio codec correspondingly so that the grounding circuit of the audio codec comes into contact with the terminal Ring2 while the audio input terminal of the audio codec comes into contact with the terminal Sleeve. Likewise, when the combo-jack of the audio apparatus uses the terminal Ring2 as the audio input terminal and uses the terminal Sleeve as the ground terminal, the designer of audio systems must design the circuit of the audio codec correspondingly so that the grounding circuit of the audio codec comes into contact with the terminal Sleeve, while the audio input terminal of the audio codec comes into contact with the terminal Ring2.
Thus, when the designer of audio systems manufactures the audio codec, the circuit design of the audio codec will be limited by the jack implementation of the combo-jack of the audio apparatus with which the audio codec is to match. Moreover, on the other hand, when a user desires to use an audio apparatus with a single combo-jack among apparatuses with different audio codecs, the user may fail to obtain the expected effect due to incompatibility between the audio codecs and the combo-jack.
In view of this, it is important to provide a circuit disposed within an audio codec, which can determine the jack implementation of a combo-jack of an audio apparatus to ensure that different combo-jacks can all operate on the audio codec normally.